A PERSON embarked on a naval
expedition, who wishes to attend to Geology, is placed in a position in
some respects highly advantageous, and in others as much to the
contrary. He can hardly expect during his comparatively short visits at
one place, to map out the area and sequence of widely extended
formations: and the most important deductions in geology must ever
depend on this having been carefully executed; he must generally
confine himself to isolated sections and small areas, in which,
however, there can be no doubt many interesting facts may be collected.
On the other hand, he is admirably situated for studying the still
active causes of those changes, which, accumulated during
long-continued ages, it is the object of geology to record and explain.
He is borne on the ocean, from which most sedimentary formations have
been deposited. During the soundings which are so frequently carried
on, he is excellently placed for studying the nature of the bottom, and
the distribution of the living organisms and dead remains strewed over
it. Again, on sea-shores, he can watch the breakers slowly eating into
the coast-cliffs, and he can

examine their action under various circumstances: he here sees that
going on in an
infinitesimally small scale, which has planed down whole continents,
levelled mountain-ranges, hollowed out great valleys, and exposed over
wide areas rocks, which must have been formed or modified whilst heated
under an enormous pressure. Again, as almost every active volcano is
situated close to, or within a few leagues of the sea, he is admirably
situated for investigating volcanic phenomena, which in their striking
aspect and simplicity, are well adapted to encourage him in his studies.

In the present state of the science, it may be doubted whether the
mere collection of fragments of rock without some detailed observations
on the district whence they are brought, is worthy of the time consumed
and the carriage of the specimens. The simple statement that one part
of a coast consists of granite, and another of sandstone or clay-slate,
can hardly be considered of any service to geology; and the labour thus
thrown away might have been more profitably spent, and thus saved the
collector much ultimate disappointment. It is now generally recognized
that both the sedimentary rocks, and those which have come from below
in a softened state, are nearly the same over the whole world. A mere
fragment, with no other information than the name of the place where
collected, tells little more than this fact. These remarks do not at
all apply to the collection of fossil remains, on which subject some
remarks will presently be made; nor do they apply to an observer
collecting suites of rock-specimens, with the intention of himself
subsequently drawing up an account of the struc-

ture and succession of
the strata in the countries visited. For this end, he can hardly
collect too copiously, for errors in the
naming of the rocks may thus be corrected, and the careful comparison
of such specimens will often reveal to him curious relations which at
the time he did not suspect.

In order to make observations of value, some reading and much
careful thought are necessary; but perhaps no science requires so
little preparatory study as geology, and none so readily yields,
especially in foreign countries, new and striking points of interest.
Some of the highest problems in geology wait on the observer in distant
regions for explanation; such as, whether the successive formations, as
judged of by the character of their fossil remains, correspond in
distant parts of the world to those of Europe and North America, or
whether some of them may not correspond to blank epochs of the north,
when sedimentary beds either were not there accumulated, or have been
subsequently destroyed. Again, whether the lowest formation everywhere
is the same with that in which living beings are first present in the
countries best known to geologists. These and many other such wide
views in the history of the world are open to any one, who, applying
thought and labour to his subject, has the good fortune to geologise in
little frequented countries.

A person wishing to commence geology, is often deterred by not
knowing the names of the rocks; but this is a knowledge, he may rely on
it, easily acquired. With half a dozen named crystalline rocks, or even
by patiently familiarizing his eye (aided by a lens) to the

aspect of
the feldspar and quartz in granite, he will know the two most essential
ingredients in most igneous rocks; and in granite he will often find
the glittering scales
of mica replaced by a dark green mineral, less hard than the feldspar
and quartz; and then he will know the third most important mineral,
hornblende. The sedimentary rocks can hardly be described, except by
the terms in common use: impure limestone, which cannot be readily
recognized by the eye, can be distinguished by its effervescence with
acids. By the repeated comparison of freshly fractured sedimentary and
igneous rocks, such as sandstone and clay-slate on the one hand, and
granite and lava on the other, he will learn the difference between
crystalline and mechanical structure; and this is a very necessary
point. Let no one be deterred from geology by the want of mineralogical
knowledge; many excellent geologists have known but little; and from
this reason its value has perhaps sometimes been underrated, for many
of the obscurer points in geology, such as the nature of the
metamorphic changes in rocks, and all the phenomena of metallic and
other veins, almost require such knowledge. The appearances presented
by the different forms of stratification (that is, the original planes
of deposition) may be soon learnt in the field; though no doubt the
beginner would be aided by the diagrams given in many elementary works.

The two most useful works which the geologist can carry with him,
are without doubt the 'Principles' and the 'Elements of Geology,' by
Sir
Charles Lyell. He should procure a treatise on mineralogy, for
instance, 'Phillips's Mineralogy,' by Allan.1 If he has the oppor-

tunity
to procure others, Sir H. Delabeche's 'Researches in Theoretical
Geology'1 would be particularly desirable from discussing many of the
questions which ought especially to engage the attention of a sea
voyager. As he will probably visit many volcanic regions, Dr. Daubeny's 'Treatise on Volcanos'2 would be extremely useful; and a list is there
given of special treatises on the volcanic countries likely to be
visited by him. The 'Description Physique des Isles Canaries,' by Von
Buch,3 may be cited as a model of descriptive powers. The voyager in the
Temperate and Polar regions ought to have Agassiz' work on Glaciers.

The geologist fortunately requires but little apparatus; a heavy
hammer, with its two ends wedge-formed and truncated; a light hammer
for trimming specimens; some chisels and a pickaxe for fossils; a
pocket-lens with three glasses (to be incessantly used); a compass and
a clinometer, compose his essential tools. One of the simplest
clinometers is that constructed by the Rev. Prof. Henslow: it consists
of a compass and spirit-level, fitted in a small square box; in the lid
there is a brass plate, graduated in a quadrant of 90 degrees, with a
little plumb-line to be suspended from a milled head at the apex of the
quadrant. The line of intersection of the edge of the clinometer, when
held horizontally, with the plane of the stratum, gives its strike,
range, or direction; and its dip or inclination, taken at right angles
to the strike, can be measured by the plumb-line. In an uneven country,
it is not easy without the clinometer to judge which is the line of
greatest inclination of a stratum; and it is always more satisfactory
to be certain of the angle than

to estimate it. A flat piece of rock
representing the general slope can usually be found, and by placing a
note-book on it, the measurement can be made very accurately. In
studying the cleavage1 or slaty structure of rocks, accurate
observations are indispensable. A mouth blow-pipe with its apparatus,
and a book with
instructions for its use (Phillips's Mineralogy contains brief
directions), teaches a little mineralogy in a pleasant manner. Besides
the above instruments, a mountain barometer is often very necessary: a
portable level would, in the case of raised sea-beaches and terraces,
be useful. Messrs. Adie and Son,2 of Edinburgh, sell a hand-level, a
foot in length, which is fitted with a little mirror on a hinge, so
that the observer, whilst looking along the level, can see when the
bubble of air is central, and thus instantly find his level in the
surrounding district. This is a very valuable instrument. Mr. R.
Chambers,3 moreover, and others have found, that an observer having
previously ascertained the exact height of his eye when standing
upright, can measure the altitude of any point with surprising
accuracy; he has only to mark by the level some recognizable stone or
plant, and then to walk to it, repeat the process, and keep an account
how many times the levelling has been repeated in ascending to the
point, the height of which he wishes to ascertain.

A few cautions may be here inserted on the method of collecting.
Every single specimen ought to be numbered with a printed number (those
which can be read upside down having a stop after them) and a book
kept exclusively for their entry. As the value of many specimens
entirely depends on the stratum or locality whence

1 Cleavage =a term used to denote the regular fissures of slaty rocks.
Foliation was a term used to describe the fissures of metamorphic schists. Darwin differed from most geologists of his day in maintaining that the fissures were not 'the constituent parts of each layer…separately deposited as sediment, and then metamorphosed.' (South America, p. 165) Instead Darwin maintained that 'in most cases foliation and cleavage are parts of the same process: in cleavage there being only an incipient separation of the constituent minerals; in foliation a much more complete separation and crystallization' (South America, p. 166. See ibid. p. 167-8.)

they were procured
being known, it is highly necessary that every specimen should be
ticketed on the same day when collected. If this be not done, in after
years the collector will never feel an absolute certainty that his
tickets and references are correct. It is very troublesome ticketing
every separate fossil from the same
stratum, yet it is particularly desirable that this should be done; for
when the species are subsequently compared by naturalists, mistakes are
extremely liable to occur; and it should always be borne in mind, that
misplaced fossils are far worse than none at all. Pill-boxes are very
useful for packing fossils. Masses of clay or any soft rock may be
brought home, if small fossil shells are abundant in them.
Rock-specimens should be about two or three inches square, and half an
inch thick; they should be folded up in paper. To save subsequent
trouble, it will be found convenient to pack up and mark outside, sets
of specimens from different localities. These details may appear
trifling; but few are aware of the labour of opening and arranging a
large collection, and such have seldom been brought home without some
errors and confusion having crept in.

To a person not familiar with geological inquiry, on first landing
on a new coast, probably the simplest way of setting to work, is for
him to imagine a great trench cut across the country in a straight
line, and that he has to describe the position (that is, the angle of
the dip and direction) and nature of the different strata or masses of
rock on either side. As, however, he has not this trench or section, he
must observe the dip and nature of the rocks on the surface, and take
advantage of every river-bank or

cliff where the land is broken, and of
every quarry or well, always carrying the beds and masses in his mind's
eye to his imaginary section. In every case this section ought to be
laid down on paper, in as nearly as possible the real proportional
scale, copious notes should be made, and a large suite of specimens
collected for his own future examination.
The value of sections, with their horizontal and vertical scales true
to nature, cannot be exaggerated, and their importance has only lately
been appreciated to the full extent. The habit of making even in the
rudest manner sectional diagrams is of great importance, and ought
never to be omitted: it often shows the observer palpably and before it
is too late (a grief to which every sea-voyager is particularly
liable), where his knowledge is defective. Partly for the same reason,
and partly from never knowing, when first examining a district, what
points will turn out the most important, he ought to acquire the habit
of writing very copious notes, not all for publication, but as a guide
for himself. He ought to remember Bacon's aphorism, that Reading
maketh a full man, conference a ready man, and writing an exact
man;
and no follower of science has greater need of taking precautions to
attain accuracy; for the imagination is apt to run riot when dealing
with masses of vast dimensions and with time during almost infinity.1 After the observer has made a few traverses of the country and drawn
his sections (and the coast-cliffs often afford him an invaluable one),
he will be himself astonished how, in the most troubled country, over
which
the surface has been broken up and re-cemented, almost like the
fragments of ice on a great river, how all the parts

fall into
intelligible order. He will in his mind see the beds first horizontally
stretched out one over the other in a fixed order, and he will then
perceive that all the disturbance has arisen from a few nearly straight
cracks, on the edges of which the beds have been upturned, and between
which he will sometimes find great wedges of once
heat-softened, but now crystalline rocks. He will find that large
masses of strata have been removed and denuded, that is ground down
into pebbles and mud, and long ago drifted away to form in some other
area newer strata. He will now have a good idea of the physical
structure of his district; and this much can be acquired with much
greater facility than he will at first readily anticipate.

In examining a district to make a section, many minor points of
detail will occur for observation, which can hardly be specified; such
as the nature and cause of the transitions and alterations of the
different strata, the source of the sediment and pebbles, the
alterations in chemical nature, either of the whole mass, or of parts,
as in concretions; the presence, and grouping and state of the fossil
remains; the depth and condition of the old sea-bottom, when the beds
were deposited, and an infinity of similar points: Probably the best
method of obtaining this power of observation, is to acquire the habit
of always seeking an explanation of every geological point met with;
for one mental query leads on to another, and this will at the same
time give interest to his researches, and will lead him to compare what
is before his eyes, with all that he has read of or seen. With his
increasing knowledge he will daily find his powers of

observation, his
very vision, become deeper and clearer. No one, however, must expect to
solve the many difficulties which will be encountered, and which for a
long time will remain to perplex geologists; but a ray of light will
occasionally be his reward, and the reward is ample.

Organic Remains.—In the sectional diagram which we have
supposed to be made, the simple superposition of
the beds gives their relative antiquity; but the best section which a
sea-voyager can hope to make, will seldom include but a small portion
of the long sequence of known geological formations. And as the voyager
seldom passes over large districts, he will rarely succeed in placing
in proper order, by the aid of superposition alone, the formations
which he successively meets with even in the same country. Hence he
must, more than any other geologist, rely on the characters of the
embedded organic remains, and must sedulously collect every specimen
and fragment of a specimen. By the means of fossil remains, not only
will he be enabled to arrange (with the help of naturalists on his
return home) the formations in the same country according to their age,
but their contemporaneity with the deposits of the most distant parts
of the world can thus and by no other method be ascertained; for it is
now known that at each geological epoch the marine animals partook in
the most distant quarters of a general similarity, even when none of
the species were identically the same: thus beds have been recognized
in North and South America, and in India, which must have been
deposited when the chalk in Europe was accumulating beneath the sea.

It is highly necessary most carefully to keep the fossils found in
different strata separate; it will often occur in passing upwards from
one bed to another, and occasionally even without any great change in
the character of the rock, that the fossils will be wholly different;
and if such distinct sets of fossils are mingled together, as if found
together, undoubtedly it would have been better for the progress of
science that they had never been collected. As there is some
inconvenience
in keeping the fossils collected on the same day separate,
this caution is the more requisite. The collector, if he be not an
experienced naturalist, should be very cautious in rejecting specimens,
from thinking them the same with what he has already got; for it
requires years of practice to perceive at once the small, but constant,
distinctions which often separate species: the same species, moreover,
if collected in different localities, or in beds one placed far above
the other, are generally more valuable to the geologist than new
species.

In formations from a few hundred to a thousand feet and upwards in
thickness, the whole of which does actually belong to the same
geological age, and is therefore characterized by the same fossils,
most curious and important results may be sometimes deduced, if the
position or relative heights at which the groups of fossils are
embedded be noted; and this is a point usually neglected. For, thanks
to the researches of Professor E. Forbes,1 the depth of water under
which a collection of shells lived can now be approximately told; and
thus the movement of the crust of the earth, whilst the strata
including the shells were accumulating, can be inferred. For instance,

if at the bottom of a cliff, say 800 feet in height, a set of shells
are buried, which must have lived under water only 50 or 100 feet in
depth; it is clear that the bottom of the sea must have sunk to have
allowed of the deposition of the 700 feet of superincumbent submarine
strata; subsequently the whole 800 feet must have been upraised. For
this same purpose, and for other ends, it is desirable that it should
be noted which species are the most numerous, and whether layers are
composed exclusively of single kinds. It should be also remarked,
whether the more delicate bivalve
shells retain their two valves united, and whether the burrowing kinds
are embedded in their natural positions, as these facts show that the
shells have not been drifted from afar. Where there are fossil corals,
it should be observed whether the greater number of specimens are
upright, in the positions in which they grew. The remark formerly made
that the collection of mere fragments of rock is of little or no use to
geology, is far from applicable to fossil remains. Every single fossil
species, bones, shells, crustacea, corals, impressions of leaves,
petrified wood, &c., should be collected, and it is scarcely
possible to collect too many specimens. Even a single species without
any information of any kind, if it prove a quite new form, will be
valuable to the zoologist; if it prove identical with, or closely
allied to a known species, it may interest the geologist. A set of
fossils, however, and still more several sets, with their superposition
known, cannot fail to be of the highest value; they will tell the age
of the deposit, and perhaps give the key to the whole geology of the
country: some of the highest problems in this

science wait for solution on large collections of species carefully
made in distant
regions.

A collection of recent shells (both those living on the coast and
those to be procured by the dredge off it) from the same country or
island at which a collection of tertiary fossil shells is made, is
generally of very great service to the palæontologist, who
undertakes
the description of the fossils. The collecting recent shells will,
moreover, with the aid of a little study, teach the geologist some
conchology, and this is an acquirement yearly becoming more necessary:
the geologist should exert himself
to learn some general zoology.

The bones of vertebrated animals are much more rarely found than the
remains of the lower marine animals, and they are almost in proportion
more valuable. A person not acquainted with the science will hardly be
able to imagine the deep interest which the discovery of a skeleton, if
of higher organization than a fish, in any of the oldest formations
would most justly create. The age of such a formation would have to be
judged of by the co-embedded shells, and therefore, if possible, part
of the slab containing the bones should include one or two shells to
demonstrate their contemporaneity. Bones, however, from any formation
are sure to be valuable; even a single tooth, in the hands of a Cuvier1 or Owen, will unfold a whole history; the heads, jaws, and articular
surfaces are the most valuable; but every fragment should be brought
home. Where bones are found close together, and especially if some of
the parts lie in their natural positions, they should be packed

1 Georges Cuvier (1769-1832), the great French systematist, comparative anatomist and palaeontologist.

together. Every bone, if found even six inches beneath the black
vegetable mould, should be collected; there can be no doubt that many
most valuable relics have been neglected, from the supposition that
they belonged to still living animals. Low cliffs of mud, gravel, and
clay on the banks of streams and on sea-shores (as well as in bared
reefs extending from them), are the most likely places for the
discovery of the remains of quadrupeds. Gravel beds under streams of
lava; fissures in volcanic rocks; peat beds, and the clay or marl
underlying peat, are all favourable places. Fishes' bones are found
occasionally in all sedimentary strata, and are highly interesting.

Caverns.—These
most frequently occur in limestone rocks, and they have yielded a truly
wonderful harvest of remains in Europe, South America, and Australia.
The bones generally occur in mud, under a stalagmitic crust produced by
the dripping of the lime-charged water, which requires being broken up
by a pickaxe. As caverns have often been used by wild races of man as
places of habitation and burial, a most careful examination should be
made to detect any signs of the surface having been anciently broken up
near where the bones are found. Even small islands, not now inhabited
by any land quadruped, if not very distant from a continent, are almost
as likely to contain osseous remains as larger tracts of land. The
interest of the discovery of the remains of land quadrupeds in an
oceanic island would be extreme: for instance, it has been stated that
the tooth of a mastodon has been found in one of the Azores; if this
were confirmed, few geologists would doubt that

these islands had once
been united to Europe, thus enlarging wonderfully our ideas of the
ancient geography of the Atlantic: so also the remains of a mastodon
are said to have been brought from Timor, thus perhaps indicating the
road by which this great quadruped formerly reached Australia.

Fossil Footsteps.—As allied to organic remains, fossil
footsteps may be here referred to. They have been observed in Europe
and North America, but hitherto in no other part of the world. These
curious vestiges not only proclaim the former existence of reptiles and
birds at very remote periods, and in rocks often not containing a
fragment of bone, but they generally prove that the level of the land
subsided after the animal had left its impress on the ancient
sea-beach, thus allowing thousands
of feet of strata to be thrown down over them. The best place for
searching for footsteps is in quarries of sandstone, in which the
strata are separated by seams of shale. The best indication of their
probable occurrence is the rock being rippled, that is marked with
narrow little wavy ridges, such as occur on most sandy shores when the
tide is down, and which indicate that the now rocky surface was once
either a tidal beach or a shallow surface, over which the ancient
animals walked. In the case of fossil footsteps being found, the
largest slab which could possibly be removed ought to be brought away,
and accurate drawings, or still better, casts, made of several of the
footsteps. A plan from accurate measurement ought to be taken of any
row of steps. The value of such fossil footsteps would be in a manifold
degree increased, if the age of the deposit could be

Coal Deposits.—The origin of coal presents a most curious
and difficult problem in geology, and though a vast amount of
information has been accumulated on the subject, yet good observations
in distant countries would be of the highest value. A very brief
statement of the most prominent difficulties in the theory of its
origin will, perhaps, be the best guide for further inquiries. If we
look first to the coal itself, the frequency with which, both in Europe
and North America, upright vegetables have been found in and on the
coal, and the curious relation between the presence of coal, and the
nature of the clayey bed (abounding with roots) on which it rests, can
leave no doubt that in these so frequent instances the vegetation,
whence the coal has
been derived, grew on the spot where now embedded. The regularity
and wide extent of the beds of coal, and especially of certain
subordinate seams in them, the stratification and fineness of the
deposits alternating with the coal, and the rarity of channels (such as
would have been formed by a stream or river) cutting through the
associated strata, all seem pretty clearly to indicate that the coal
was not formed on the surface, like a mass of peat, but under water.
What, then, was the nature of those vast expanses of shallow water
under which the coal was accumulated? The character of the upright
fossil plants, according to our present knowledge, absolutely
contradicts the idea of their having lived in the sea; yet occasionally
strata, containing undoubted marine remains, are associated with the
carboniferous series.

On the other hand, how can we believe that lakes,
allowing of course their beds slowly to sink, could contain the
enormous thickness, amounting in some instances to several thousand
yards, of the coal-bearing strata? From these few remarks it will
be seen how many points deserve careful examination in any new
coal district; the chief points being, the presence of upright
vegetables and trunks of trees (of the position of which careful
drawings should be made), and whether furnished with roots,—the nature
of the beds on which the coal rests, and generally of all the strata;
the continuousness and form of the strata, and whether ripple-marked;
the existence of marine animal remains, and whether such lived on the
spot, or were drifted into their present positions, and many other
similar points. It is superfluous to observe that all fossil plants
should be collected; those found upright should be carefully
distinguished from those embedded horizontally. The contents of any
upright stems and of the roots should be examined; as it appears they
have generally first become hollow from decay, and then been filled up
with mud, which in some instances is charged with seeds and leaves.

Salt Deposits.—Information is much required on this
subject; and this is a case in which good suites of specimens,
illustrating the nature of the rocks beneath and above the salt, would
possess much interest. Do they contain any organic remains? Did such
live on the spot where now buried? Do the rocks show signs of having
undergone in any degree the action of heat? Are the strata regular, or
are they crossed by oblique layers, showing the probable action of
currents? Are there ripple-

marks, or beds of coarse pebbles, or other
indications of the strata having been deposited in shallow water? What
is the thickness, form, and dimensions of the beds of salt? Specimens
of the salt, and of any associated saline substances, ought to be
brought home in bottles for analysis. The origin of beds
of salt, found in formations of very different ages in different parts
of the world, is at present quite obscure; some authors attribute it to
the sinking of superficial sea-water, rendered more saline by
evaporation; others to the evaporation of sea-water periodically
overflowing extensive low sandy tracts, like parts of the Run of Cutch;1 others suspect that its deposition is in some unknown way connected
with the sea's bottom having been heated by volcanic action. In some
countries there are large lakes of brine, often covering thick beds of
salt; these deserve examination: on what does such salt or brine rest,
whether on the bared underlying strata, or on sand or gravel, such as
cover the surrounding country? Does the salt contain the remains of
animals or plants? Specimens of the salt ought to be brought home in
bottles, and attention paid, whether beneath it there is any thin layer
of other saline substances.

Cleavage.—The slaty structure of rocks will at first
perplex the young geologist; for in proportion as it becomes well
developed, the planes of stratification or of original deposition
become obscure, and are often quite obliterated. As the sea-voyager,
and especially the surveyor, often visits numerous points on the same
line of coast, he possesses some great advantages for studying this
subject, and numerous observations made with care

would probably give
striking results. The range or strike of the cleavage is uniform over
surprisingly large areas; whereas both the angle and point of dip
varies much; but there is reason to believe that the planes of
inclination, examined across a wide tract transversely to the range,
will fall into order and show that they are the truncated edges of a
few great curves or domes. The relation of the cleavage-planes to those
of the stratification, or axes of elevation, should be carefully noted,
and likewise to the general outline of the whole country. Long sections
at right angles to the strike of the cleavage, with the dip carefully
protracted on paper, would be highly interesting. When two chains of
hills, each having its independent cleavage, cross each other, careful
observations should be made. In all cases, any mineralogical
difference, however slight, in the parallel cleavage-layers, deserves
attention; but observations on this head would be hardly trustworthy,
without the planes of stratification were so distinct that there could
be no possibility of confounding (as has often happened) cleavage and
stratification. Where a stratum of sandstone, or of any other rock
without cleavage, is interstratified with a slaty rock, the surface of
junction ought to be minutely examined, to see if the slate has slipped
along the planes of cleavage, or whether again the mass has not been
either stretched or compressed at right angles to these same planes.
Fossil shells have been found by Mr. Sharpe1 in slaty rocks, which have
had their shapes greatly altered, and all in the same direction; here
then we have a guide to judge of the amount and direction of the
mechanical

displacement which the surrounding slate-rocks have
undergone.* Observations on cleavage, to be useful, must be numerous
and very accurately made.

The foliation of the metamorphic schists, that is, the origin of the
layers of quartz, mica, feldspar, and other minerals, of which gneiss,
micaceous, chloritic, and hornblendic schists are composed, is
intimately connected with the cleavage of homogeneous slaty rocks.
Nearly all the proposed observations on cleavage are applicable to
foliation. Wherever large districts of foliated and ordinary slaty
rocks unite, observations would be most desirable. These foliated rocks
have all undergone metamorphic action, that is, they have been
mineralogically altered and rendered crystalline by chemical
attraction, aided by heat; but this is a most obscure subject,
one on which it would appear that much further light will not be thrown
without the aid of a profound knowledge of mineralogy or chemistry. It
is now known that granitic rocks, which have been fluidified (as may be
told by their sending great veins into, and including fragments of, the
overlying rocks), are foliated in a more or less perfect degree: in
these cases the relation of the planes of foliation with those of the
adjoining rocks, which have been metamorphosed but not fluidified,
would be eminently curious.

Nature of the Sea-bottom.—As every sedimentary stratum has
once existed as the bed of the sea or of a lake, the importance of
observations on this head is obvious;

* With respect to further observations on this
important point, Mr. Hopkins remarks, in his paper 'On the Internal
Pressure of Rock Masses' (Cambridge Philosoph. Transact., vol. viii.),1 that the observer should direct his attention especially to those
cases in which the inclination of the cleavage planes to the bedding is
either small, or nearly 45°.

and no one is so favourably
circumstanced for making them as a naval officer on a surveying
expedition. The limits of depth under different latitudes at which the
various marine animals live or are found strewed dead, is perhaps the
most important point for further investigation which can be suggested
in the science of geology: scarcely any observations with the dredge
have been made within the tropics. Not only the shells, corals,
sea-urchins, crabs, &c., brought up
from different stated depths, should be preserved, but the
proportionate numbers of each kind be carefully noted, as well as the
nature of the sea-bottom. An observer could not labour too much in this
line, and especially if he would subsequently himself undertake to
tabulate and work out the results.*

There is another point of view under which the bed of the sea would
amply repay long-continued observations. It is well known that the
nature of the bottom often changes very regularly in approaching a
coast; the pebbles, for instance, increasing in size in a surprisingly
steady ratio with the decreasing depth. But the means by which the
pebbles are thus sorted is not known: is it by the oscillation of the
waves at ordinary periods, or only during gales; or is it by the action
of currents? A chart, with the nature of the bottom carefully noted on
it and the currents laid down, would by itself throw some light on this
question. The nature of the pebbles being observed, perhaps a point
would be found whence they radiated. Excellent observations have been
made by engineers on the travelling of shingle-beaches, but scarcely
anything is

* The best kind of dredge, and the manner of using
it, are described under the Zoological Section.

known of their movement under water. In what condition are
the pebbles?—are they encrusted (as often happens) with delicate
corallines—after a heavy gale are the spines of such corallines found
broken? In narrow channels where there are rapid currents, and in the
open sea in front of straits, where the water often suddenly deepens,
what is the nature of the bottom? To what depth does the sea in a storm
render the water
muddy? How far from the beach, and to what depth, does the recoil of
the waves, or the undertow, act, for instance, on light anchors? At
what depth can the sea wear solid rock? This may sometimes be judged of
by the nature of the bottom; thus, where soft mud overlies the rocky
surface, we may infer that the sea can hardly now be a destroying
agent, even if the inclination of the strata on the adjoining coast
shows that rocky strata must once (probably, when the land stood at a
different level) have extended much further. Is it at the line of high
or low water, or between
them, that the breakers most vigorously eat into coast-cliffs?
Gigantic fragments of rock, much too large to be themselves rolled
about, may be seen at the foot of almost every line of high cliffs; by
what means in the course of time will these be removed, as must have
happened with their innumerable predecessors? Are they slowly worn away
or broken up? It may be well to recollect that in the tropics the
powerful action of frost in splitting stones is entirely eliminated.
Our observations, moreover, on the alluvial and sub-littoral deposits
of these latitudes are not perplexed by the ancient effects of floating
ice. The spray of salt-water, above the line of breakers, corrodes by

chemical decomposition calcareous rocks; does this play any
important
part on other rocks? Most bold coasts are fronted by sharp promontories
and even isolated pinnacles; are these exclusively due to
the greater hardness of the rocks composing them, or do not the
breakers act more efficiently when eddying round any slight projection?

Rocks rising steeply out of the open ocean, and exposed to the
incessant wash of the heaviest surf, are often thickly coated over with
various marine animals, and this would seem to indicate that pure water
has not the power of gradually wearing away hard rocks, though the
waves may occasionally tear off large fragments. Is the washing to and
fro of pebbles, or of sand, a necessary element in the corroding power
of waves on hard rocks? but how comes it that small land-locked
harbours, where the waves can hardly have force to move the shingle,
should ever be surrounded by cliffs, which, in most cases, clearly
prove that considerable masses of rock have been worn down into mud and
removed? Again, at a moderate depth, where the bottom is covered with
shingle, does the rolling to and fro of the pebbles wear away solid
rock? if so, the pebbles would be clean, and the submarine rocky
surface probably worn into furrows or channels at right angles to the
beach. Where there are violent currents and eddies, are deep round
holes worn in the bottom, like those produced by eddies at the foot of
cascades? This, perhaps, might be ascertained by a long pole at the
turn of the tide: deep round holes have been observed on rocks formerly
covered by the sea, and their origin has perplexed geologists.

Any
person steadily attending to these subjects will occasionally be
enabled to form an opinion on points at first appearing hopelessly
obscure to him. The common deep-sea lead, especially if made a little
bell-shaped and well armed, gives a surprisingly good picture of the
bottom. There can be no doubt that whoever will for a long period
collect and compare observations, made over wide areas and under
different
circumstances, will arrive at many curious, novel, and important
results.

An
observer occasionally may arrive at a district where lately some great
aqueous catastrophe has occurred, such as the bursting of a lake
temporarily formed by a slip, or the rush of a great earthquake-wave
over low land. In such cases all the effects produced, such as the
thickness and nature of any deposit left—whether stratified irregularly
or continuously—whether any rocky surface, over which the debacle has
passed, be scored or smooth; all such points should be minutely
described, and measurements taken of any great blocks which may have
been transported: the great desideratum is accuracy and minuteness.

Ice Action.—The voyager in the Polar Seas would render an
excellent service to geology by observing all the effects which
icebergs produce in rounding, polishing, scoring, and shattering solid
rocks, and likewise in transporting gravel and boulders. Floating ice
under two forms is known to transport fragments; namely, coast-ice, in
which the stranded boulders are frozen, and icebergs formed by glaciers
entering the sea, on the surface of which masses of rock had previously
fallen from the surrounding precipices. It is obvious that in the
latter case

the fragments would generally be quite angular, and they
could not be landed in water shallower than the thickness of the
submerged ice, requisite to float the berg. On the other hand, the
boulders frozen in coast-ice would generally be previously water-worn,
and they could be landed on an ordinary beach, and might be driven by
the force of the pack high and dry, and perhaps left piled in strange
positions. All facts illustrating the difference
in the results produced by coast-ice and true icebergs would be very
valuable. Do the boulders fixed on coast-ice, when driven over rocky
shoals, become themselves scored? Wherever there was reason to believe
that a surface had been scored by recent ice-action, a minute
description and drawings ought to be made of the depth, length, width,
and direction of the grooves; and even large slabs brought home. On
true icebergs are the fragments of rock generally fixed or loose; when
icebergs turn over, are fragments frequently seen embedded in that part
which was under water; and how were they fixed there? The nature,
number, size, form, and frequency of occurrence of all fragments of
rock seen on floating ice ought to be recorded, and the distance from
their probable source. A polar shore, known from upraised organic
remains to have been lately elevated, would be eminently instructive.
Do great icebergs force up the mud and gravel at the bottom of the sea
in ridges like the moraines of glaciers? Can shells, or other marine
animals, live in a shallow sea, often ploughed up and rendered turbid
by the stranding of icebergs? The dredge alone could answer this. The
means to distinguish the effects of ancient floating ice

from those
produced by ancient glaciers is, at present, a great desideratum in
geology. M. Agassiz' work on Glaciers,1 with its admirable plates, ought
to be procured by any one going to the colder regions of the north or
south.

Erratic boulders occur in Europe, N. America, and in the southern
parts of S. America, which, it is believed by most geologists, were
transported by ice; those near mountains, by ancient glaciers; and
those on the lowlands, by floating ice. Erratic boulders, when not of
gigantic size, may be confounded with rounded stones, transported by
occasional great floods or by the coast-action of the surf during slow
changes of level of the land. Masses of granite, from often
disintegrating into large, apparently water-worn boulders, and then
rolling downwards, have several times been erroneously described as
belonging to the erratic class. Where the nature of all the rocks
in the vicinity is not perfectly known, great size and the angularity
of the fragments (though by no means a constant concomitant) are the
most obvious distinctive characters; but even when the surrounding
country is not at all known, the composition of a single isolated hill
or small island may easily be ascertained, and if large fragments of
foreign rock lie strewed on its surface, these may be assumed almost
certainly to be erratic boulders. Here, however, a caution has been
found necessary; for in the case of fragments of sedimentary rocks,
they may be the last remnant of a denuded overlying formation. Wherever
erratic boulders are found, their composition, form—especially
attending to whether they are angular, water-worn, or scored, and

Both in the north and south a peculiar formation called till has
been found connected with erratic boulders; it consists generally of
mud, containing angular and rounded stones of all sizes up to the
largest boulders, mingled in utter confusion, and generally without any
stratification. Such deposits should be examined. Sometimes when they
are stratified, the upper beds have been found violently contorted,
whilst the lower ones are undisturbed, showing that the violence has
not
proceeded from below, as in ordinary geological cases. Sir C. Lyell has
suggested that this effect has been produced by the stranding of great
icebergs.

As far as our present knowledge goes, the above enumerated
phenomena—such as scored, mamillated, and polished rocks, moraines,
erratic boulders, and beds of till, though occurring in latitudes where
glaciers do not now occur, where the sea is never frozen, and where
icebergs are never drifted, yet have not been observed in either
hemisphere higher than about latitude 40°. Hence, on whatever coast
ancient ice-action might be discovered, the limit of latitude towards
the tropics at which it ceases ought to be carefully investigated.
Observations are much wanted on the west coast of N. America and the
east coast of Asia; and again in New Zealand and other islands of the
Southern Ocean. The period of the ice-action is pretty well ascertained
in Europe and North America, and a very great service would be rendered
to geology if the same point could be clearly made out in the southern
hemisphere; for it might greatly influence our

ideas on the climate of
the world during the late tertiary periods. Any shells embedded in
till (though, unfortunately, of very rare occurrence) would decide
this point, and it might probably be closely judged of, if till or
boulders were found resting on, or covered by, shell deposits.

Distribution of Organic Beings.—As geology includes the
history of the organic inhabitants, as well as of the inorganic
materials, of the world, facts on distribution come under its scope.
Earth has been observed on icebergs in the open ocean; portions of such
earth ought
to be collected, washed with fresh-water, filtered, gently dried,
wrapped up in brown paper, and sent home by the first opportunity to be
tried, with due precautions, whether any seeds still alive are included
in it. Again, the roots of any tree cast up on an island in the open
ocean should be split open, to see if any earth or stones are included
(as often happens), and this earth ought to be treated like that from
icebergs: it is truly surprising how many seeds are often contained in
extremely small portions of earth. Any graminivorous bird, caught far
out at sea, ought to have the contents of its intestines dried for the
same object. The zoologist who, with a towing-net, fishes for floating
minute animals, ought to observe whether seeds are thus taken. These
experiments, though troublesome, undoubtedly, would be well worth
trying. All facts or traditional statements by the inhabitants of any
island or coral-reef, on the first arrival of any bird, reptile,
insect, or remarkable plant, ought to be collected. In those rare cases
in which showers of fish, reptiles, shells, earth, seeds,
confervæ,
&c., have fallen from the sky, every fact should be recorded, and
specimens collected.

ample
opportunities of examining volcanic islands, and perhaps volcanoes in
eruption. With respect to the latter, he ought to record all that he
sees: should the exact position of the orifice be known, he might,
perhaps, by observing some point in a cloud, measure with a sextant to
what height the fragments were shot forth, and the height of the often
flat-topped column of ashes. Having surveying instruments, he ought to
map, as carefully as time will permit, any crater remarkable for its
size, depth, or peculiar form. M. Élie de Beaumont has found
that,
owing to the fluidity of lava, streams never consolidate into a thick,
moderately-compact mass, except on a surprisingly gentle inclination.
On a slope of above 2 or 3°, the stream consists of extremely
irregular masses, often forming a hollow vault within. Fresh
observations on this point are much wanted in regard to lavas of
different composition. The measurements can easily be made by a sextant
and artificial horizon.* In

The method I am in the habit of employing for these
kinds of measurements is simple and easy, and a description of it may
save useless trouble to others. I place on the edge of the sextant, and
behind the fixed mirror, a small piece of white paper, in which there
is a narrow opening (ouverture étroite) corresponding to the
axis of the telescope. On the exterior surface of the paper a black
line is drawn, perpendicular to the plan of the graduated circle, and
passing through the centre of the opening above mentioned. A quantity
of mercury is poured into a vessel sufficient to form a plane
horizontal surface of a certain extent. The telescope of the sextant is
then directed vertically over the mercury, and the image of the black
line sought for. When this is found, I am certain that the visual ray
from the image in the mercury can only deviate from the perpendicular,
in so far as the line is not without breadth, and the opening has a
sensible size. These two sources of error can be diminished so that the
maximum of error shall not exceed a minute. Being once certain of the
verticality of the visual ray from the

making such observations, comparatively
recent streams must be chosen, so that there can be no doubt that the
whole consists of a single stream: this cannot be judged of without
examining the whole line between the two points of
measurement, for some liquid lavas thin out to a very fine edge; and
two streams, one over the other, may be thus very easily mistaken for a
single one. The composition, thickness, and degree of cellularity of
any lava-stream, of which the slope is measured, ought to be described
as seen on the sides of fissures, and wherever its internal structure
can be made out.

Round many active and extinct volcanoes, both on continents and on
islands, there is a circle of mountains, steep on their inner, and
gently inclined on their outer flanks. The volcanic strata, of which
they are composed, everywhere dip away from the central space, but at a
considerably higher angle than it is believed lava can consolidate into
such thick and compact masses. These mountains form the so-called
craters of elevation, the origin of which has excited much
controversy, and which demand further examination. There is a grand
range of mountains of this class at the Mauritius and at St. Jago in
the Cape de Verdes, parts only of which have been described. The chief
points to attend to are, the inclination of the streams by
actual measurement, their thickness, compactness, and composition; the
form and height of the mountains, whether traversed by
very many dikes,

image of the black line, I have
only to make the image of any object reflected from the moveable mirror
coincide with that of the black line, to have the angle between the
vertical, and the line drawn from the centre of the instrument to the
object in question, which may be any distant point on the surface of a
bed of lava, a glacier, a road, a river, &c.

of which the common
direction ought to be recorded;
how far the mountains stand apart, and the diameter and outline of the
rude circle which they together form. In fact, a most useful service
would be rendered by mapping any of
these craters of elevation, or, what would be more feasible, drawing
from actual measurements two sections at right angles to each other,
across the circle.

Some streams of lava, especially those belonging to the trachytic
series (harsh, generally rather pale-coloured lavas, with crystals of
glassy feldspar), are laminated. The course of the layers with respect
to the course of the stream ought to be minutely studied, both on the
surface, at the termination, and flanks of the stream; and, if by a
most fortunate chance there should have been formed a transverse
section, throughout its entire thickness: this would be a very
interesting subject for investigation. A series of specimens ought to
be brought away to illustrate the nature of the lamination.

Aerial Dust.—Fine brown-coloured dust has often fallen on
vessels far out at sea, more especially in the middle of the Atlantic.
This should be collected; the direction and force of the wind (and the
course of any upper current, as shown by the movement of the clouds) on
the same day, and for some previous days, ought to be recorded, as well
as the date, and the position of the ship. Such dust has been shown by
Ehrenberg1 to consist, in many cases, almost entirely of the siliceous
envelopes of infusoria. The distance to which real volcanic dust is
blown is, likewise, in some respects well worth determining.

accompanying earthquakes, will be treated of by Mr. Mallet,1 but a few
remarks on the nature of the evidence to be sought, on changes of level
not actually witnessed by man, may be here inserted. Many appearances,
such as
lines of inland cliffs, of sand-hillocks, eroded rocks, and banks of
shingle, often indicate the former effects of the sea on the land when
the latter stood at a lower level. But the best evidence, and the only
kind by which the period can be ascertained (for the appearances above
enumerated, though well preserved, may sometimes be of considerable
antiquity), is the presence of upraised recent marine remains. On land
which has been elevated within a geologically recent time, sea shells
are often found, either embedded in thin layers of sand and mould, or
scattered on the bare surface. In these cases, and especially in the
latter case, great caution is requisite in testing the evidence; for
man, birds, and hermit-crabs often transport, in the course of ages, an
extraordinary number of shells. In the case of man, the shells
generally occur in heaps, and there is reason to believe that this
character is long preserved. To distinguish the shells transported by
animals from those uplifted by the movement of the earth, the following
characters may be used:—Whether the shells had long lain dead under
water, as indicated by barnacles, serpulæ, corallines adhering to
their insides; whether the shells, either from not being
full grown or from their kind, are too small for food; remembering that
certain shells, as mussels, may be unintentionally transported by man
or other animals in their young state adhering to larger shells; and
lastly, whether all the specimens have the same appearance of
antiquity. Some

shells, which have been exposed for many ages, yet
retain their colours in a surprising manner. The very best evidence is
afforded by barnacles and boring shells being found attached to or
buried in the
rock, in the same positions in which they had lived; these may be
sometimes found by removing the earth or birds' dung covering points of
rock. Where shells are embedded in a superficial layer of soil, though
it may appear exactly like vegetable mould, specimens of it should be
preserved, for the microscope will sometimes reveal minute fragments of
marine animals. In all these cases, specimens of the shells, though
broken and weathered, and having a wretched appearance, must carefully
be preserved; for a mere statement that such upraised shells resembled
those still living on the beach is absolutely of no value. It should be
noticed whether the proportional numbers between the different kinds
appear to be nearly the same in the upraised shells and in those now
cast on the beach. The height at which the marine remains occur above
the level of the sea should be measured. In confined situations where
the change of level appears to have been small, much caution must be
exercised in receiving any evidence; as a change in the direction of
the currents (resulting from alterations in neighbouring submarine
banks) may cause the tide to flow to a somewhat less height, and thus
give the appearance of the land having been upraised.

Wherever a tract of country can be proved to have been recently
elevated, its surface, as exhibiting the late action of the sea, is a
fertile field for observation. On such coasts, terraces rising like
steps, one above another, often occur. Their outline and composition
should be

studied, diagrams made of them, and their height measured at
many and distant parts of the coast. There is reason to believe that in
some instances such
terraces range for surprisingly long distances at the same height.
Where several occur on opposite sides of a valley a spirit level is
almost indispensable, in order to recognize the corresponding stages.
Where ranges of cliffs exist, the marks of the erosion of the waves may
sometimes be expected to occur, and as these generally present a
defined line, it is particularly desirable that their horizontality
should be ascertained by good levelling instruments, and if not
horizontal, that their inclination should be measured. Where more than
one zone of erosion can be detected all should be levelled, for it does
not necessarily follow that the several lines are parallel. Along
extensive coasts, and round islands which have been uplifted to a
considerable height, and where we now walk over what was, within a late
geological period, the bed of the sea, it would be well to observe
whether extensive sedimentary deposits have been upraised; for it has
often been tacitly assumed that sedimentary deposits are in process of
formation on all coasts.

Subsidence of the Land.—This movement is more difficult to
detect than elevation, for it tends to hide under water the surface
thus affected. Evidence, therefore, of subsidence is very valuable; and
this movement, moreover, has probably played a more important part in
the history of the world than elevation, for there is reason to believe
that most great formations have been accumulated whilst the bed of the
sea was sinking. Subsidence may sometimes be inferred from the form of
the coast-land;

for instance, where a line of cliffs, too irregular to
have been formed by elevation alone, plunges precipitously into a sea
so profoundly deep that it cannot be supposed that the now deeply
submerged
portions of the cliff have been simply worn away by the currents. The
direct evidence of subsidence, if not witnessed by man, is almost
confined to the presence of stumps of trees, peat-beds, and ruins of
ancient buildings, partly submerged on tidal beaches. Ancient buildings
may sometimes afford such evidence in unlikely situations: it has been
asserted, that in one of the volcanic islands in the Caroline
archipelago there are ruins with the steps covered by the sea. Again,
at Terceira, at the Azores, there is an old church or monastery said to
be similarly circumstanced.

Coral Reefs.*—The most important point with respect to
coral reefs, which can be investigated, is, the depth at which the
bottom of the sea, outside the reef, ceases to be covered
with a continuous bed of living corals. This can be ascertained by
repeated soundings with a heavy and very broad bell-shaped lead, armed
with tallow, which will break off minute portions of the corals or take
an exact impression of them: it can thus also instantly be seen how
soon the bottom becomes covered with sand. This limit of depth ought to
be ascertained in different seas, under different latitudes, and under
different exposures. For collecting specimens of the corals, it is to
be feared that the dredge would become entangled, but chains and hooks
may be lowered for this purpose. There is reason to suspect that
different species of corals

grow in different zones of depth; so that
in collecting specimens, the depth at which each kind is found, and at
which it is most abundant, should be carefully noted. It ought always
to be recorded whether the specimen came from the tranquil waters of
a lagoon or protected channel, or from the exposed outside of the reef.
The small reefs within the lagoons of certain atolls (or
lagoon-islands) in the Indian Ocean all rise to the surface; whereas in
other atolls not a single reef rises within several fathoms of the same
level. It would be a curious point to ascertain whether the corals in
these cases consisted of the same species; and if so, on what possible
circumstance this singular difference in the amount of their upward
growth has depended.

Any facts which can elucidate the rate at which corals can grow
under favourable circumstances, will ever be interesting: nor should
negative facts, showing that within a given period reefs have not
increased either laterally or vertically upwards, be neglected. In a
full-grown forest, to judge of its rate of growth, a part must be first
cut down; so is it probably with reefs of corals. The aborigines of
some of the many coral islands in the great oceans might perhaps adduce
positive facts on this head; for instance, the date might be known when
a channel had been cut to float out a large canoe, and which had since
grown up.

For the classification of coral reefs, the most important point to
be attended to, is the inclination of the bed of the adjoining sea;
and, secondly, the depth of the interior lagoon in the case of atolls,
and of the channel between the land and the reef, in Encircling or
Barrier, and in

Fringing reefs. Whenever it is practicable, soundings
ought to be taken at short ascertained distances, from close to
the breakers in a straight line out to sea, so that a sectional outline
might be protracted on paper. In those cases in which the bottom
descends
by a set of ledges or steps, their form ought to be particularly
attended to; and whether they are covered with sand or by dead or
living coral; and whether the corals differ on the different ledges:
the same points should be attended to within the lagoon, wherever its
bed or shore is step-formed: the origin of these steps or ledges is at
present obscure. In the Indian and Pacific Oceans there are entire
reefs, having the outline of atolls or lagoon-islands lying several
fathoms submerged; there are likewise defined portions of reefs both in
atolls and in encircling reefs similarly submerged. It would be
particularly desirable to ascertain what is the nature of these
submerged surfaces, whether formed of sand or rock or living or dead
corals. In some cases two or more atolls are united by a linear reef;
the form of the bottom on each side of this connecting line ought to be
examined. Where two atolls or reef-encircled islands stand very near
each other, the depth between them might be attempted by deep
soundings: the bottom has been struck between some of the Maldiva
atolls. Generally the form and nature of the reefs encircling islands
ought to be compared in every respect with the annular reefs forming
atolls.

On the shores of every kind of reef, especially of atolls and of
land encircled by barrier reefs, evidence of the slow sinking of the
land should be particularly sought for;

for instance, by stumps of
trees, the foundation-posts of sheds, by wells or graves or other works
of art, now standing beneath the level of high-water mark, and which
there was good reason to believe must have once stood above its level.
The observer must bear in mind that cocoa-nut trees and mangroves will
grow in salt-water. If such evidence be found, inquiry ought to be made
whether earthquakes have been felt. On the other
hand, all masses of coral standing so much above the level of the sea
that they could not have been thrown up by the breakers during gales of
wind, at a period when the reef had not grown so far out seaward,
should be investigated and their height measured. There is reason to
believe that some coral-reefs have been thought to have been upraised,
owing to the effect of the lateral or horizontal extension of the reefs
having been overlooked; for the necessary result of this outward growth
is gradually to break the force of the waves, so that the rocks, now
further removed from the outer breakers, become worn to a less height
than formerly, and the more inland corals not being any longer
constantly washed by the surf, cease to live at a level at which they
once flourished. It is indispensable that specimens of all upraised
corals, and especially of the shells generally associated with them,
should be collected; for there can be no doubt that ancient strata
containing corals, have in some instances been confounded with recent
coral-rock. The importance of ascertaining whether coral-reefs have
undergone, or are undergoing, any change of level, depends on the
belief that all the characteristic differences between Atolls and
Encircling reefs on the one hand, and

Fringing reefs on the other,
depend on the effect produced on the upwardly-growing corals by the
slow sinking or rising of their foundations.

A thick and widely-extended mass of upraised recent coral-rock has
never yet been accurately examined, and a careful description of such a
mass—especially if the area included a central depression, showing that
it originally existed as an atoll—is a great desideratum.
Of what nature is the coral-rock; is it regularly stratified or
crossed by oblique layers; does it consist of consolidated fine
detritus or of coarse fragments, or is it formed of upright corals
embedded as they grew? Are many shells or the bones of fish and turtle
included in the mass, and are the boring kinds still in their proper
positions? The thickness of the entire mass and of the principal strata
should be measured, and a large suite of specimens collected.

In conclusion, it may be re-urged that the young geologist must bear
in mind, that to collect specimens is the least part of his labour. If
he collect fossils, he cannot go wrong; if he be so fortunate as to
find the bones of any of the higher animals, he will, in all
probability, make an important discovery. Let him, however, remember
that he will add greatly to the value of his fossils by labelling every
single specimen, by never mingling those from two formations, and by
describing the succession of the strata whence they are disinterred.
But let his aim be higher: by making sectional diagrams as accurately
as possible of every district which he visits (nor let him suppose that
accuracy is a quality to be acquired at will), by

collecting for his
own use, and carefully examining numerous rock-specimens, and by
acquiring the habit of patiently seeking the cause of everything which
meets his eye, and by comparing it with all that he has himself seen or
read of, he will, even if without any previous knowledge, in a short
time infallibly become a good geologist, and as certainly will he enjoy
the high satisfaction of contributing to the perfection of the history
of this wonderful world.